Special Issue "Modified Theories of Gravity and Cosmological Applications"

A special issue of Universe (ISSN 2218-1997). This special issue belongs to the section "Gravitation".

Deadline for manuscript submissions: 31 May 2021.

Special Issue Editors

Prof. Panayiotis Stavrinos
Website
Guest Editor
Department of Mathematics, National and Kapodistrian University of Athens, Athens, Greece
Interests: modified gravity; cosmology; gravitational waves; Finsler Cosmology; extended Friedmann Equations; dark matter; inflation; dark energy
Prof. Dr. Emmanuel N. Saridakis
Website
Guest Editor
1. Physics Department, Baylor University, Texas 76798-7316, USA
2. Physics Department, National Technical University of Athens, 15780 Zografou Campus, Athens, Greece
Interests: dark energy formulation; modified theories of gravity; inflationary cosmology; brane cosmology; observational cosmology
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Special Issue Information

Dear Colleagues,

General Relativity is a theory of gravity that describes with high accuraacy some of the effects of gravity, such as solar system tests, gravitational lensing, gravitational waves, black holes, etc., in a definite framework of an homogeneous and isotropic space-time.

However, taking into account the abundance and nature of dark energy and dark matter, the nature of inflation, cosmological tensions such as the H0 and S8, the possible values of local anisotropy in the evolution of the universe, as well as the theoretical problems of the cosmological constant and of nonrenormalizability, the validity range of general relativity might be restricted.

Modified theories of gravity extend the form of general relativity through various methods, leading to different field equations and thus to different comsological implications. They play an essential role in and contribute to modern cosmology, providing a foundation for the current understanding of physical phenomena of the Universe.

Among the other topics included are the following:

Alternative theories of gravity and General Relativity;

Scalar-Tensor theories;

Finsler Cosmology;

Modified Telleparalel gravity;

Extra-dimensional theories of gravity;

Early and late times applications of modified gravity;

Effects of modified gravity on gravitational waves observations;

Modified gravity and cosmological tensions.

This Special Issue wishes to contribute to these efforts; we invite colleagues to submit their manuscripts.


Prof. Panayiotis Stavrinos
Prof. Dr. Emmanuel N. Saridakis
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Universe is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Gravitation
  • General Relativity
  • Modified gravity
  • Cosmology

Published Papers (3 papers)

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Research

Open AccessArticle
Photon Spheres, ISCOs, and OSCOs: Astrophysical Observables for Regular Black Holes with Asymptotically Minkowski Cores
Universe 2021, 7(1), 2; https://doi.org/10.3390/universe7010002 - 22 Dec 2020
Cited by 5
Abstract
Classical black holes contain a singularity at their core. This has prompted various researchers to propose a multitude of modified spacetimes that mimic the physically observable characteristics of classical black holes as best as possible, but that crucially do not contain singularities at [...] Read more.
Classical black holes contain a singularity at their core. This has prompted various researchers to propose a multitude of modified spacetimes that mimic the physically observable characteristics of classical black holes as best as possible, but that crucially do not contain singularities at their cores. Due to recent advances in near-horizon astronomy, the ability to observationally distinguish between a classical black hole and a potential black hole mimicker is becoming increasingly feasible. Herein, we calculate some physically observable quantities for a recently proposed regular black hole with an asymptotically Minkowski core—the radius of the photon sphere and the extremal stable timelike circular orbit (ESCO). The manner in which the photon sphere and ESCO relate to the presence (or absence) of horizons is much more complex than for the Schwarzschild black hole. We find situations in which photon spheres can approach arbitrarily close to (near extremal) horizons, situations in which some photon spheres become stable, and situations in which the locations of both photon spheres and ESCOs become multi-valued, with both ISCOs (innermost stable circular orbits) and OSCOs (outermost stable circular orbits). This provides an extremely rich phenomenology of potential astrophysical interest. Full article
(This article belongs to the Special Issue Modified Theories of Gravity and Cosmological Applications)
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Open AccessCommunication
Constructing Higher-Dimensional Exact Black Holes in Einstein-Maxwell-Scalar Theory
Universe 2020, 6(9), 148; https://doi.org/10.3390/universe6090148 - 09 Sep 2020
Cited by 1
Abstract
We construct higher-dimensional and exact black holes in Einstein-Maxwell-scalar theory. The strategy we adopted is to extend the known, static and spherically symmetric black holes in the Einstein-Maxwell dilaton gravity and Einstein-Maxwell-scalar theory. Then we investigate the black hole thermodynamics. Concretely, the generalized [...] Read more.
We construct higher-dimensional and exact black holes in Einstein-Maxwell-scalar theory. The strategy we adopted is to extend the known, static and spherically symmetric black holes in the Einstein-Maxwell dilaton gravity and Einstein-Maxwell-scalar theory. Then we investigate the black hole thermodynamics. Concretely, the generalized Smarr formula and the first law of thermodynamics are derived. Full article
(This article belongs to the Special Issue Modified Theories of Gravity and Cosmological Applications)
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Open AccessCommunication
Spinning Test Particle in Four-Dimensional Einstein–Gauss–Bonnet Black Holes
Universe 2020, 6(8), 103; https://doi.org/10.3390/universe6080103 - 28 Jul 2020
Cited by 56
Abstract
In this paper, we investigate the motion of a classical spinning test particle in a background of a spherically symmetric black hole based on the novel four-dimensional Einstein–Gauss–Bonnet gravity [D. Glavan and C. Lin, Phys. Rev. Lett. 124, 081301 (2020)]. We find that [...] Read more.
In this paper, we investigate the motion of a classical spinning test particle in a background of a spherically symmetric black hole based on the novel four-dimensional Einstein–Gauss–Bonnet gravity [D. Glavan and C. Lin, Phys. Rev. Lett. 124, 081301 (2020)]. We find that the effective potential of a spinning test particle in this background could have two minima when the Gauss–Bonnet coupling parameter α is nearly in a special range 8<α/M2<2 (M is the mass of the black hole), which means a particle can be in two separate orbits with the same spin-angular momentum and orbital angular momentum, and the accretion disc could have discrete structures. We also investigate the innermost stable circular orbits of the spinning test particle and find that the corresponding radius could be smaller than the cases in general relativity. Full article
(This article belongs to the Special Issue Modified Theories of Gravity and Cosmological Applications)
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